P0300 why would a car only have this code?

Hi,

A P0300 indicates a random misfire. This can be caused by a few things. Since you indicated it runs good other than a minor stumble at idle, my first suspect would be an engine vacuum leak or the need for a tune-up.

Has the vehicle been tuned up with new spark plugs recently? It should be done by 100K. If it has, then I need you to check for engine vacuum leaks. Here is a link that explains how to do it:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know what you find or if you have other questions.

Take care,

Joe